| Acid Rain (1 tracked article) |
| Biofuels (2 tracked articles) |
| Biological Products (988 tracked articles) |
| Colloids (36 tracked articles) |
| Fossil Fuels (8 tracked articles) |
| Freund's Adjuvant (1 tracked article) |
| Lignin (8 tracked articles) |
| Manure (1 tracked article) |
| Particulate Matter (58 tracked articles) |
| Radioactive Pollutants (2 tracked articles) |
| Soil (39 tracked articles) |
| Tissue Extracts (2 tracked articles) |
| Vehicle Emissions (5 tracked articles) |
| Venoms (17 tracked articles) |
| Waste Products (20 tracked articles) |